Extensible hydraulic supports



y 1961 B. TEBB ET AL 2,985,418

EXTENSIBLE HYDRAULIC SUPPORTS Filed Oct. 2, 1959 In ven tors Be el/172DTie 5 6417454105 #Marer Elegy w By United States Patent EXTENSIBLEHYDRAULIC SUPPORTS Bernard Tebb, Swanland, and Clarence Herbert Perry,

Hull, England, assignors to Mastabar Mining Equipment Company Limited,Hull, England, a British com- P y Filed Oct. 2, 1959, Ser. No. 843,977

Claims priority, application Great Britain Oct. 29, 1958 2 Claims. (Cl.2.48354) This invention concerns extensible hydraulic supports of thetype, such as hydraulic pit props, which comprise an outer tubularmember, an inner tubular member provided or formed at its lower end witha piston or ram working in a pressure chamber presented by said outermember, and hydraulic release and yield valves adapted respectively toenable said support to be collapsed from an extended condition and toenable said support fractionally and repeatedly to yield on theapplication thereto of a load in excess of a predetermined maximum load,said collapsing and yielding operations taking place by said valvesallowing hydraulic medium from the pressure chamber to exhaust to areservoir usually constituted by. the interior of the inner tubularmember above the piston thereof.

In hydraulic supports of this type, it is desirable for maintenancepurposes to have the valve mechanisms at the outer or uppermost end ofthe ram tube, Where they can be easily replaced if necessary, and oneconvenient way of arranging said valves is in a head piece locatedwithin and sealing the ram tube, and serving also as a location forextension tubes which may have to be employed e.g. at a coal face, onaccount of varying roof to floor height. Where a head piece is provided,then it is usual for the valves therein to communicate with the pressurechamber by way of a hydraulic conduit or tube passing down the ram tubeand secured at one end to said head and at the other end to the ram orpiston, the necessary connections between the head, the hydraulicconduit and the ram being effected by welding, brazing or screwing, or acombination of all three.

However, hydraulic supports in operation are subjected to substantialdegrees of loading, for example, in a typical hydraulic pit prop, thenormal loading applied to the inner or ram tube is of the order of 20/25tons, and under such conditions compression of the ram tube takes place,to the extent of some 0.001 inch per ton of applied load. Consequently,due to this compression, the jointing of the hydraulic conduit or tubeto the head and ram of the ram tube frequently develops faults.

It is an object of the invention to provided means for overcoming thisdisadvantage.

According to the present invention, in a hydraulic support of the typedescribed, the hydraulic conduit connected between the ram and the headpiece of the inner tubular member is fixedly arranged at one end only,and the other end of said conduit is arranged to permit relativedisplacement to occur between said other end and either the ram or thehead piece, as the case may be.

Preferably the relative displacement is Permitted by way of a slidableconnection between the end concerned of said hydraulic conduit and theram or the head piece, to whichever it is connected, although a flexibleconnection such as a flexible tube between the two may alternatively beemployed. Where a slidable connection is used, the hydraulic conduit ispreferably fixedly seice cured at its lower end to the ram and at itsupper end engages slidingly with a short tube or probe fixed to andextending from the head piece of the inner tubular member of thesupport, a suitable seal being provided circumferentially'between saidhydraulic conduit and said short tube or probe.

Thus, in the construction proposed by the invention, since the hydraulicconduit is fixedly jointed at one end only, the head piece may readilybe removed from the ram tube (i.e. the inner tubular member) forservicing or replacement of the valves therein, and, even moreimportant, the compression load experienced by the ram tube is notapplied to the said joints.

The invention will be described further by way of example with referenceto the accompanying drawing, in which the single figure is a sectionalelevation through a hydraulic pit prop embodying the invention.

In the drawing on outer tubular member 10 is telescopically engaged bythe inner tubular member 12 provided at its lower end with a ram orpiston 14. The interior 16 of the inner tubular member or ram tube 12constitutes a reservoir for hydraulic medium, and the space 18 of theouter tubular member 10, below the piston 14, constitutes a workingchamber to which hydraulic medium under pressure is transferred fromreservoir 16 as described below.

The upper face of the prop piston 14 has secured thereto, a cylinder 20within which is reciprocable a pump piston '22 displaceable by aconnecting rod 24 extending axially through the reservoir 16 so as to bereciprocated by a crank 26 having a driving member 28 extending throughthe wall of the ram tube 12 for manual operation externally thereof. Theprop piston 14 is provided with pump intake and delivery passages andvalves (not shown) for enabling hydraulic medium to be transferred fromthe reservoir 16 to the pressure chamber 18.

The upper end of the ram tube 12 is closed by a head piece 30 which alsoserves as a convenient means for locating a replaceable extension piece32 adapted to bear against the roof of a mine working and having itslength chosen to accord with the prevailing roof to floor height.

To enable a pit prop such as that described above either to be collapsedfrom an extended condition or momentarily to yield should the roof loadapplied thereto exceed a predetermined maximum value, the pit prop isprovided with hydraulic medium relief and release valves 34 and 36respectively adapted to allow momentarily relief of the pressureobtaining in pressure chamber 18 and to allow said pressure to collapsecompletely, in both instances by allowing transfer of the hydraulicmedium from the chamber 18 through passages 38 and 40 of the prop pistonor ram 14, a hydraulic conduit 42, and into passages '44 and 46 in thehead piece 30 and respectively communicating with the rehef valve 34 andthe release valve 36. The communication of the passage 44 with therelief valve 34 will be seen to be by way of a filter 35 for thehydraulic medium. The relief valve 34 may be of any convenientconstruction adapted for the purpose, and, as shown, is preferablyincorporated in a removable capsule, whilst the release valve 36 isshown in the drawing as being a ball valve member adapted for unseatingby a plunger 48 displaceable by a pivotal lever 50 which in turn isadapted to be rocked if an outward pull is exerted on a movable abutment52 incorporated in the pump actuating member 28.

In conventional constructions of hydraulic supports, the hydraulicconduit 42 is fixedly jointed at one end to the head piece 30 and at theother end to the prop piston 14, and when compression of the innertubular member 12 takes place in consequence upon the high load appliedthereto, it has been found that faults frequently develop in such fixedjoints and/ or in the hydraulic conduit 42.

The invention therefore provides that onlythe lower end of the hydraulicconduit 42 is fixedly jointed to the prop piston 14 so as to communicatewith the passages 38 and 40, whilst the upper end of the hydraulicconduit 42 isrbell-mouthed or otherwise suitably formed or enlarged toslidingly receive a hollow probe 54- depending from the head piece 30,said probe 54 communicating With the passages 44 and 46 of the headpiece 30. The probe 54 may be secured or jointed to the head piece 30 inany convenient conventional manner, as by welding, brazing or screwing,and is provided with an oil seal 56 to prevent any leakage ofpressurized oil from the conduit 42 when the prop is under pressure. Theoil seal 56 may be an O-ring or any other suitable conventional typeseal. Thus, in the construction shown in the drawing, not only may thehead piece 30 readily be removed from the inner tubular member 12 of thepit prop when maintenance of the valves 34 or 36 is required, but evenwhen the ram tube 12 is subjected to physical compression under loadedconditions, the compression load is relieved from the joint of the probe54 with head piece 30 and from the joint of the hydraulic conduit 42with the piston 14 due to the ability of the conduit 42 of the probe 54to slide relative to one another. The only stresses then required to betaken into account are the usual bursting stress on the conduit 42 dueto the pressure of hydraulic medium therein, and the end load exerted bysaid pressure on the probe 54. This end load, however, is relativelysmall, and is more than balanced by the load on the prop tending to seatthe head piece 30 on the ram tube.

We claim:

1. In a hydraulic support of the type comprising an outer tubular memberprovided at its lower end with a closure member, an inner tubular memberprovided at its lower end with a closure member in the form of a ramengaged within said outer member, the space in said outer member belowsaid ram constituting a pressure chamber, and the interior of said innermember above said ram constituting a reservoir for hydraulic medium, asecond closure member in the form of a head piece sealing the upper endof said inner member, a hydraulic medium release valve, a hydraulicyield valve, said valves both being arranged in said second closuremember, and a hydraulic conduit extending between said two closuremembers to enable said valves to communicate with said pressure chamber,the improvement wherein said hydraulic conduit is fixedly secured by oneof its ends to only one of said closure members, and the other end ofsaid conduit terminates short of the other one of said closure members,a hollow probe extending from said other closure member to engageslidably in sealing relation in said other end of said conduit and asealing ring of circular cross section surrounding a free end region ofsaid probe to engage within and seal said hydraulic conduit.

2. A hydraulic support as set forth in claim 1, wherein one end of thehydraulic conduit is fixedly secured to the ram and said hollow probeextends from said head piece.

References Cited in the file of this patent UNITED STATES PATENTS371,919 Belden Oct. 25, 1887 1,886,621 Bagwill Nov. 8, 1932 2,477,533Whiting July 26, 1949 2,621,631 Dowty Dec. 16, 1952 2,693,223 Krupp Nov.2, 1954 m in-b

